1. Field of the Invention
This invention relates to a coupling device and a power device responsive to establishment of the coupling for supplying electrical power, and more particularly to such devices of the sort suited to cameras.
2. Description of the Related Art
Of the conventional devices for connecting and disconnecting an electrical power source to and from a circuit, there is what is employed in, for example, the interchangeable lens type of cameras. The camera of this type comprises a body having the electrical power source or battery and, for example, a first microcomputer incorporated therein, and a lens unit releasably attached to the body and having incorporated therein a second microcomputer and electric motors for driving the diaphragm and the focusing lens, wherein it is the common practice that an interconnection terminal as the outlet of the battery and another interconnection terminal which is on the lens unit are arranged upon attachment of the lens unit to the body to be brought into direct contact with each other to establish a power line.
In such a conventional camera, however because as will be understood from above the power supply is started just when the two interconnection terminals come to contact with each other even if the lens unit is in detachment from the body, a battery voltage is always left to appear at the interconnection terminal on the body. Hence, it has been very likely that the voltage is accidentally applied to an adjacent interconnection terminal of a signal line. If so, it can destroy the first microcomputer. This has contributed to a defect of the reliability of the camera.
An attempt has been made to eliminate such a problem by disposing the faces of the terminals of the power and signal lines out of a common circle with its center at the optical axis either axially or radially so that the terminals on the lens unit are permitted to contact only with the corresponding ones on the body thereby the signal line is prevented from shorting out.
However, the use of this structure calls for a large increase of the space the interconnection terminal assembly occupies. Within the limited space, therefore, only a few terminals can be placed. If the number of terminals is increased to a desired value, the size of the camera would be caused to increase. Also, if the camera body without the lens unit is let stand alone, because the faces of the terminals are all exposed to the air and the power line is always supplied with the current from the battery, there is some possibility of occurrence of a shorting out of the signal line if it happens that a metal piece bridges over them. For such reasons, the above-described problem has not basically been overcome.
A technique for insuring the safety in the supply of electrical power by means of preventing the shorting out between the camera body and the lens unit has been proposed in U.S. Pat. application Ser. No. 877,264 filed June 23, 1986 and assigned to the assignee of the present invention where the terminal end of coupling of the lens unit with the camera body is detected by a mechanical switch, and, in that state, the microcomputers in the lens unit and body respectively are then allowed to communicate with each other in a prescribed scheme. Only after that, the battery voltage starts to appear at the power line to the motor.
The conventional coupling devices, among others, those suited particularly to the interchangeable lens type cameras have been known in many forms. Of these, the typical one which is leading the recent fashion in the field of art is illustrated in FIG. 7. The camera body 1 and the lens unit 2 have respective coupling members or mounts 3 and 16. A lock pin 12 is arranged in the camera body to enter a detect hole 13 provided in the lens unit under the action of a bias spring 14 when the coupling of the lens unit 2 with the camera body 1 is complete, thereby the lens unit 2 is hindered from rotating relative to the camera body 1. Thus, the coupling device is locked. To detach the lens unit 2 from the camera body, the camera user needs first to push down an operating member until the lock pin 12 retracts from the hole 13, and then to turn the lens unit 2 to a prescribed angular position where the coupling members 3 and 16 disengage from each other.
Here, during the attaching and detaching of the lens unit 2 to and from the camera body 1, the lock pin 12 slides not only at its end face on the lens side mount 16, but also at its peripheral surface on the wall of the hole 13 when the locking and unlocking take place. Therefore, as the number of times the interchanging of the lens unit 2 is repeated increases, the lock pin 12 and the lens side mount 16 are worn out, giving rise to a problem in that the accuracy of adjustment of the locked angular position of the lens unit 2 relative to the camera body is so largely decreased and the axial looseness between the mounts 3 and 16 is so largely increased as not to assure the correct alignment and the intimate contact of the electrical interconnection terminals on the camera body 1 and the lens unit 2 with each other when in the coupled position. Besides this, because it is only by the lock pin 12 that the lens unit 2 is held on the camera body 1 in the direction of rotation, if, as the lens unit 2 is turned to tighten relative to the camera body 1, a strong force is applied to it, the locking means 12 and 13 is deformed or broken with a high possibility.